Abstract
Low Density Parity Check (LDPC) codes have been selected to provide channel coding for data in the next generation of wireless communication standard referred to in practice as the 3GPP New Radio (NR). In contrast to the LDPC codes adopted in previous standards, the NR LDPC code can be considered to be a concatenation of a core LDPC code and a Low Density Generator Matrix (LDGM) code. This particular feature has the advantage of offering flexible coding rate, but it prevents the application of conventional extrinsic information transfer (EXIT) chart analysis. This article characterizes this problem and addresses it using a novel reinterpretation of the NR LDPC factor graph. Based on this factor graph, a novel 3D EXIT chart technique is conceived for our three-stage scheme, which facilitates the visual characterisation of the NR LDPC decoder's iterative decoding convergence process for the first time. The proposed EXIT chart analysis accurately visualizes the mutual information exchange amongst the components of the NR LDPC decoder, which was not facilitated by the conventional 2D EXIT chart. We demonstrate the power of this technique by using it to design a novel iterative decoding activation order for the NR LDPC decoder, which reduces the decoding complexity by approximately 17% compared to a conventional flooding decoder. This is achieved without degrading its error correction capability. We conclude by discussing several other opportunities for exploiting the proposed 3D EXIT chart technique to improve the design of concatenated LDPC and LDGM codes.
Highlights
Channel coding is a fundamental element in modern wireless communication system, since it facilitates an infinitesimally low Bit Error Ratio (BER) at near-capacity spectral and/or power efficiencies
1) In order to fix the failure of conventional EXtrinsic Information Transfer (EXIT) chart analysis for the New Radio (NR) Low Density Parity Check (LDPC) code, we propose a novel reinterpretation of its factor graph that is more suitable for EXIT chart analysis
4) In order to demonstrate the capability offered by our novel EXIT chart analysis, we show that by using the most appropriate decoding component activation order, our scheme imposes a lower complexity than a conventional LDPC decoder based on a flooding schedule
Summary
Channel coding is a fundamental element in modern wireless communication system, since it facilitates an infinitesimally low Bit Error Ratio (BER) at near-capacity spectral and/or power efficiencies. We will demonstrate that the presence of these degreeone variable nodes prevents the application of conventional EXtrinsic Information Transfer (EXIT) chart analysis [4] for characterising the iterative decoding convergence of the NR LDPC code It prevents the use of EXIT charts as a powerful tool of characterising the capacity-approaching capability [5] of the NR LDPC code, or for designing the iterative decoding activation order [6] or the control of early termination strategies [7], for example. 2) Based on this factor graph, a novel pair of more detailed 3D EXIT charts are produced by treating the LDPC and LDGM parts of the PCM separately We show that these 3D EXIT charts correctly visualize the iterative convergence of the NR LDPC decoder.
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